P38 magazine:

ENM 15a variation 

Magazines of the 15th type are marked on the left side of the magazine housing with the letters a or b. The meaning of these letters is not known, but some collectors speculate that these magazines were issued with early a- and b-block suffix Spreewerk pistols. These magazines are marked with the Spreewerk Waffenamt E/88 on the spine. No stamps were applied that indicate the ENM factory as the manufacturer. However, the elongated, rectangular welding spots are consistent with ENM production.

These magazines were issued only with early Spreewerk pistols. These magazines are considered rare among P.38 collectors.